1. Field of the Invention
The invention relates to a vehicular control device and a vehicular control method for a vehicle in which power is transmitted to driving wheels via an automatic transmission.
2. Description of the Related Art
For example, in a vehicle employing an internal combustion engine as a power source, a driving force generated thereby is transmitted to a drive shaft via an automatic transmission. In order to stop such a vehicle with the automatic transmission in a running (D) range in which a driving force is transmitted to the drive shaft, a driver or the like of the vehicle usually performs an operation of depressing a brake pedal or the like so as to prevent the vehicle from moving forwards due to a creeping force. In this state, the engine carries out work corresponding to a load of the creeping force. Fuel consumed to carry out the work constitutes a major factor leading to a deterioration in practical fuel consumption in the engine installed in the vehicle as a whole.
In order to reduce an amount of fuel consumed during such stoppage of the vehicle in the D range, there is known an art in which a target rotational speed of a control device for controlling an operational state of the engine is reduced during stoppage of a vehicle in a D range (Japanese Patent Application Laid-Open No. 10-115237). However, reduction of a target rotational speed of an engine during stoppage of a vehicle in a D range through adoption of such an art also affects stability of an idling state. In this case, namely, although fuel consumption is improved, the engine is not always in its desirable operational state. Especially when an auxiliary requiring a large load such as an onboard air-conditioner or the like is driven, there is also an apprehension that stability of an idling state will deteriorate.
Further, in order to reduce an amount of fuel consumed during stoppage of the vehicle in the aforementioned D range, there is also known an art wherein so-called neutral control, which is designed to set an automatic transmission in a substantially neutral state for inhibiting generation of a creeping force, is performed under a predetermined condition (e.g., Japanese Published Patent No. 63-35869). By performing this neutral control during stoppage of the aforementioned vehicle in the D range, the amount of fuel consumed due to generation of an unnecessary creeping force is reduced. Therefore, practical fuel consumption in the engine installed in the vehicle as a whole is enhanced.
In a vehicle mounted with an engine in which the aforementioned neutral control is performed, various engine control operations such as adjustment of an amount of intake air or adjustment of timings for opening or closing valves in the engine are usually performed as well with a view to operating the engine more efficiently or at a higher output. That is, while an output of the engine is determined depending on circumstances in which the engine control operations are performed, a load applied to the engine is determined depending on circumstances in which the aforementioned neutral control is performed. Accordingly, if the aforementioned neutral control is performed irrespective of circumstances in which the engine control operations are performed, stable operation of the engine may become impossible owing to fluctuations in load applied to the engine.
The status quo described hitherto generally holds true not only for a vehicle employing an internal combustion engine as a power source but also for a vehicle which is provided with an automatic transmission and a power source and in which the performance of the aforementioned neutral control brings about fluctuations in load applied to the power source.